In-wheel motor

Abstract

To provide an in-wheel motor that improves radiation performance by using a flow of a wind caused by a traveling wind.SOLUTION: An in-wheel motor of the present invention is an in-wheel motor housed in an inside of a wheel, the wheel comprising: a tire mounting part to which a tire is mounted; and an annular fin that is formed on an outer circumferential surface the in-wheel motor and forms a flow channel for air flow between the fin and the tire mounting part.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an in-wheel motor.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2014-177167 (Patent Document 1) describes an outer-rotor type in-wheel motor (Summary and Paragraph 0008). That is, this in-wheel motor includes an annular rotor core that is a rotor, a magnet fixed to the inner peripheral surface side of the rotor core, and a case that covers the outer periphery of the rotor core. The case has fins standing radially on the outer surface of the bottom surface, and when the in-wheel motor is disposed inside the wheel, the bottom surface of the case faces the front portion of the wheel, and a flow path that connects the front space and the rear space of the in-wheel motor is formed between the inner peripheral surface of the wheel and the outer peripheral surface of the case.

[0003] As described above, since the fins are formed on the case, the case not only acts as a heat radiator but also acts as a centrifugal fan. Further, since the case covers the outer periphery of the rotor core and a flow path that connects the front space and the rear space of the in-wheel motor is formed, an air flow in which air outside the wheel passes through the wheel via the outer peripheral surface of the case is generated by the centrifugal fan action. Due to this air flow, new outside air is continuously introduced between the fins, and the heat dissipation effect by the fins is enhanced (Paragraph 0009).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the cooling structure of Patent Document 1, cooling is performed by the flow due to the centrifugal fan effect when the wheel rotates, and the influence of the traveling wind is not considered.

[0006] An object of the present invention is to improve the heat dissipation performance by utilizing the flow of wind due to the traveling wind in an in-wheel motor.

Means for Solving the Problems

[0007] In order to achieve the above object, the in-wheel motor of the present invention is an in-wheel motor housed in a wheel, and the wheel includes a tire mounting portion on which a tire is mounted, and an annular fin formed on an outer surface in the circumferential direction of the in-wheel motor and forming a flow path through which air flows between the tire mounting portion.

Effects of the Invention

[0008] According to the present invention, in an in-wheel motor, it is possible to improve the heat dissipation performance by utilizing the flow of wind due to the traveling wind.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] In the following description, the configuration according to the present invention and the configuration according to the comparative example of the present invention will be described. The same reference numerals are given to the same configurations to avoid duplication of the same description. Also, when there are differences in the configurations with the same reference numerals, those differences will be described.

Example

[0011] With reference to FIGS. 1 and 2, an in-wheel motor 1 according to an embodiment of the present invention will be described. FIG. 1 is a cross-sectional image view of the in-wheel motor 1 according to an embodiment of the present invention as viewed from the vehicle traveling direction. FIG. 2 is a perspective cross-sectional view of the in-wheel motor 1 according to an embodiment of the present invention.

[0012] The in-wheel motor 1 includes, as components, a stator 2, a rotor 3, and a rotor housing 4. Although a power conversion device (not shown) may be disposed inside the rotor housing 4, in this embodiment, the power conversion device is mounted on the vehicle body side. The stator 2 has a stator core 21 and a coil 22, and the rotor 3 has a rotor core 31 and a magnet 32. In this embodiment, the rotor core 31 is disposed on the outer peripheral side of the stator core 21 such that the inner peripheral surface thereof faces the inner peripheral surface of the stator core 21. The stator core 21 is supported from the inner diameter side by a stator housing (not shown). That is, the inner peripheral surface of the stator core 21 is covered by the stator housing. The coil 22 is wound around the stator core 21. The winding method of the coil 22 is not limited, such as concentrated winding, distributed winding, or alpha winding. Also, the wire of the coil 22 may be either round wire or flat wire.

[0013] The stator 2 and the rotor 3 are arranged such that the outer peripheral surface of the rotor core 31 faces the inner peripheral surface of the stator core 21, that is, an inner rotor configuration is excluded from the scope of the present invention.

[0014] The power conversion device performs a switching operation to convert the DC power supplied from a battery (not shown) into three-phase AC power. This three-phase AC power is supplied to the stator winding of the stator 2, and a rotating magnetic field is generated in the stator 2. Due to the rotating magnetic field generated in the stator 2, the rotor 3 is rotationally driven.

[0015] The in-wheel motor 1 is housed inside the inner peripheral side of the wheel 5 and is connected to the wheel 5 via the rotor housing 4. The wheel 5 includes a tire mounting portion 51 and a central portion 52. In this embodiment, the outer peripheral surface of the rotor core 31 is fixed to the inner peripheral surface of the central portion 52 by shrink fitting, an adhesive, a leaf spring, bolts, or the like.

[0016] The wheel 5 is manufactured by press forming or drawing of steel-based materials, or casting, die casting, forging, machining, etc. of light metals such as aluminum. It may be integrally formed, or may be divided into 2 to 3 parts in the axial direction, assembled after molding. Different from conventional wheels, there are no spokes for supporting the vehicle weight and transmitting rotation, and the rotor housing 4 also serves as a spoke.

[0017] A tire 6 is mounted on the wheel 5. The tire 6 is selected from commercially available conventional tires that are suitable for the rim diameter and rim width of the wheel.

[0018] The rotor housing 4 is manufactured by casting, die casting, forging, machining, etc. of light metals such as aluminum. It may be manufactured by press forming or drawing of steel-based materials, but casting or die casting of light metals is desirable because it is difficult to form the cooling fins described later. Since it is the boundary between the inside of the in-wheel motor 1 and the atmosphere and has a dust and waterproof function, it is desirable to be integrally formed. In this embodiment, since heat dissipation from the outer surface of the rotor housing 4 to the atmosphere is assumed, the material of the rotor housing 4 is required to have a high thermal conductivity. Although high thermal conductivity resins etc. are also candidates, metals are desirable from the viewpoint of thermal conductivity. As an example, the maximum thermal conductivity of a high thermal conductivity resin is about 5 W / (m·K), while the thermal conductivity of aluminum is about 240 W / (m·K).

[0019] The rotor housing 4 is composed of a cylindrical portion 41 and a side plate portion 42 that seals the space between the wheel 5 and an axle (not shown). An annular fin 43 is formed on the cylindrical portion 41, and a plurality of radial fins 44 are formed on the side plate portion 42. Heat is transferred from the motor heating parts such as the core and coil to the cylindrical portion 41 or the side plate portion 42, and finally dissipated into the atmosphere through the fins. Therefore, from the viewpoint of heat conduction, it is desirable that the annular fin 43 and the radial fins 44 are integrally formed with the cylindrical portion 41 and the side plate portion 42.

[0020] The annular fin 43, the tire mounting portion 51 of the wheel 5, and the annular region surrounded by three sides of the cylindrical portion 41 form the annular flow path 431. In a structure where the rotation axis is stationary and rotates in place, air does not flow into the annular flow path 431 and the cooling effect is weak. However, in the case of something like a tire that rotates and moves in the vehicle traveling direction, traveling wind flows into the flow path, resulting in a higher cooling effect.

[0021] Two adjacent radial fins 44 and the radial region surrounded by three sides of the side plate portion 42 form the radial flow path 441. A radial flow 451 is generated by the centrifugal fan. When the rotor housing 4 rotates, the air in the radial flow path 441 is pushed out to the outer peripheral side by centrifugal force, and new air flows into the radial flow path 441 from the inner peripheral side. This air flow is called the centrifugal fan effect, and heat is transferred from the radial fins 44 to the air in the radial flow path 441 due to this air flow. In a structure where the rotation axis is stationary and rotates in place, the same wind speed and the same heat dissipation amount are obtained in all the radial flow paths 441. However, in the case of something like a tire that rotates and moves in the vehicle traveling direction, in front of the tire, the flow in the radial flow path and the traveling wind are in opposite directions, so the wind speed becomes slow. Details will be described later with reference to FIG. 4.

[0022] Although not shown in FIGS. 1 and 2, the rotor 3 is provided with a rotation axis. In the following description, the direction along the axis of the rotation axis will be referred to as the "axial direction" for explanation. Also, the "circumferential direction" and the "radial direction" shall indicate the "circumferential direction" and the "radial direction" of the in-wheel motor 1 (stator core, rotor core) unless otherwise specified.

[0023] Figures 3 and 13 are enlarged cross-sectional views of the annular fin 43 according to an embodiment of the present invention. The annular fin 43 is formed on the outer circumferential surface of the in-wheel motor 1 in the circumferential direction, and forms an annular flow path 431 through which air flows between the tire mounting portion 51. The radial fins 44 are radially formed on the outer circumferential surface of the in-wheel motor 1 in the axial direction. In this embodiment, the radial fins 44 extend in the radial direction and are connected to the annular fin 43. That is, the outermost side in the radial direction of the radial fins 44 is larger than the inner diameter of the annular fin 43 and equal to or less than the outer diameter, and the radial fins 44 and the annular fin 43 are configured to be connected.

[0024] In this way, the radial fins 44 are connected to the annular fin 43, become longer along the radial direction, the centrifugal force increases, the flow velocity in the radial flow path 441 improves, and accordingly the heat transfer rate from the radial fins 44 to the atmosphere improves. Further, by connecting the annular fin 43 that improves the radial rigidity of the cylindrical portion 41 and the radial fin 44 that improves the axial rigidity of the side plate portion, when considered as a beam model, the support at the end of the side plate portion 42 becomes closer to a fixed support from a pin support and the rigidity improves. As a result, it leads to an improvement in the heat transfer rate of the radial fins 44 and an improvement in the rigidity around the connection portion between the cylindrical portion 41 and the side plate portion 42. Therefore, the cooling efficiency is increased, the material of the housing can be changed, and it is also possible to provide a lightweight and high-rigidity rotor housing.

[0025] Next, as shown in FIG. 3, the annular fin 43 is disposed axially inward of the outermost peripheral portion of the side plate portion 42 of the housing of the in-wheel motor 1. As a result, the radial flow path 441 becomes longer as described above, leading to an improvement in the heat transfer rate of the radial fins 44 and an improvement in the rigidity around the connection portion between the cylindrical portion 41 and the side plate portion 42.

[0026] Further, as shown in FIG. 13, an inclined surface portion 42a is formed between the side plate portion 42 and the cylindrical portion 41. When air flows through the radial flow path 441, the pressure becomes low on the radially outer side of the inclined surface portion 42a, so the air flows along the inclined surface portion 42a. By making this portion an inclined surface instead of a right angle, the heat transfer coefficient of the inclined surface portion is increased due to the flow along the inclined surface. If it were a right angle, the flow would not follow along the cylindrical portion 41 (the flow would turn at a right angle), and near the cylindrical portion 41, the flow would separate and remain at a low pressure, resulting in little improvement in the heat transfer coefficient of the cylindrical portion 41.

[0027] Due to this inclined surface, the heat transfer coefficient of the radial fins 44 is improved, leading to an improvement in the heat dissipation performance. The angle formed by the inclined surface portion 42a and the side plate portion 42 is preferably 45 degrees or less. The smaller this angle, the less separation of the flow in the radial flow path 441 (the flow separating from the wall and the pressure becoming low near the wall), so the heat transfer coefficient of the inclined surface portion 42a is further improved.

[0028] FIG. 4 is an image diagram of the wind received by the tire. In the case of something like a centrifugal fan that rotates in place without the rotation axis moving, the flow rate and flow velocity of all the radial flow paths are uniform. On the other hand, in the case of something like a tire that moves in the vehicle traveling direction while rotating, considering natural wind, it receives a traveling wind (headwind) with the same wind speed as the traveling direction speed. Due to rotation, the relative speed with the surrounding air at the outer periphery of the tire becomes the circumferential speed T. Above the tire, since the circumferential speed is in the same direction as the traveling direction, the relative speed with the surrounding air becomes 2T, which is twice the circumferential speed T (= traveling speed). Below the tire, since the circumferential speed is in the opposite direction to the traveling direction, the relative speed with the surrounding air is zero.

[0029] FIG. 5 is an image of the wind flow near the in-wheel motor 1. As described above, above the rotor housing 4, the flow velocity of the traveling wind is high and the influence on heat transfer is large. Therefore, by forming a circumferential flow path, that is, an annular flow path 431, in this portion, the flow velocity in the flow path can be increased and the heat dissipation performance can be improved. On the other hand, from the front to above, since the wind flow in the radial flow path 441 and the traveling wind are opposed, the cooling effect of the radial flow path 441 decreases.

[0030] Behind the rotor housing 4, since the flow of the wind in the radial flow path 441 and the traveling wind are in the same direction, the influence of the radial flow due to the centrifugal fan effect becomes greater. Below the rotor housing 4, since the relative velocity in the traveling direction becomes low, cooling by the traveling wind cannot be expected, but it is cooled by the radial flow.

[0031] In this way, above the rotor housing 4 where the flow velocity relatively increases due to the movement of the tire, it is cooled by the circumferential flow in the annular flow path 431, and behind the wheel where the circumferential flow is small, it is cooled by the radial flow in the radial flow path 441. Thus, the heat transfer coefficient is improved by the fins along the air flow, and the cooling effect is enhanced.

[0032] Figure 6 is a cross-sectional view taken along the arrow A-A in Figure 5. Generally, the axial width of the tire 6 is larger than the axial width of the tire mounting portion 51. For this reason, when viewed from the front in the traveling direction, the annular flow path 431 is hidden by the tire 6 and cannot be seen. However, like the wings of an airplane, as shown by the arrow in the figure, the traveling wind flows along the tire 6 and the wheel 5. This is because if the traveling wind expanded by the axial width of the tire 6 flows straight to the rear, the vicinity of the annular fins 43 of the wheel 5 would become a low pressure, and due to the pressure difference, the traveling wind would be bent and flow along the contour. When looking at the cross-section of the tire 6, it is streamlined and flows into the annular flow path 431 without separation or the like.

[0033] Figure 7 is an analysis example of the traveling wind at a speed of 30 km / h. It shows the streamline of the flow velocity. From the front to the upper part, the flow in the annular flow path is large, and it can be confirmed that the traveling wind flows into the annular flow path 431 from the front and flows up to the upper part. At the rear, it can be confirmed that the flow in the annular flow path 431 is almost absent and the flow velocity in the radial flow path 441 is large. In this analysis example, it is modeled with only the tire and wheel, but even if fenders, suspension arms, etc. are considered, the flow conditions in the annular flow path 431 and the radial flow path 441 generally do not change.

[0034] Figures 8 to 11 show modified examples of the radial fins 44. Figure 8 is an example in which fins of the same length are arranged radially around the rotation axis.

[0035] Figure 9 shows a modified example in which fins of different lengths are arranged alternately. By adopting this configuration, the length of the fin 44a can be increased, leading to an increase in the surface area, and it can also function as a reinforcing rib on the inner diameter side that requires structural strength. If all the radial fins are made long, the interval between the fins becomes narrow on the inner diameter side, and the number of fins cannot be increased. However, by combining short fins 44b, the number of radial fins on the outer diameter side that enhance the centrifugal fan effect can be increased.

[0036] Figure 10 shows a modified example in which the fins are arranged obliquely with respect to the radiation. By arranging them obliquely, the length of the fins can be increased, leading to an increase in the surface area. Also, in the region from the front to the upper side, the radial flow and the running wind are less likely to oppose each other, so the flow velocity in the radial flow path 441 increases and the heat dissipation performance improves.

[0037] Figure 11 shows a modified example in which the outer diameter side of the radial fin is made into an arc. The flow of the wind near the outlet of the radial flow path 441 becomes smooth, leading to an improvement in the flow velocity and a reduction in the wind loss due to rotation.

[0038] Figures 8 to 11 are examples of the embodiments and do not limit the structure. Also, it is possible to configure them by combining each of them.

[0039] Figure 12 shows an image of mounting on a two-wheeled vehicle. As shown in the figure, the in-wheel motor 1 may be mounted on the front and rear wheels, or only on the front wheel or only on the rear wheel. In addition to two-wheeled vehicles, it is applicable to an in-wheel motor 1 of a type in which the rotor housing 4 is exposed on the outermost surface. For example, small mobility can be considered. In the case of a four-wheel in-wheel motor 1, from the viewpoints of maintenance and compatibility, it is common to cover the outside of the in-wheel motor 1 with a conventional wheel, so it cannot be applied to a structure where such running wind does not directly hit. As described above, by cooling the upper part of the wheel where the relative flow velocity becomes high due to the movement of the tire by the circumferential flow in the annular flow path, the cooling performance can be improved.

[0040] Note that the present invention is not limited to the above-described embodiments, and various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations. Also, it is possible to add, delete, or replace a part of the configuration of the embodiment with another configuration.

Explanation of Reference Numerals

[0041] 1... In-wheel motor, 2... Stator, 3... Rotor, 4... Rotor housing, 6... Tire 41... Cylindrical portion, 42... Side plate portion, 43... Annular fin, 431... Annular flow path, 44... Radial fin, 441... Radial flow path, 5... Wheel, 51... Tire mounting portion, 52... Central portion

Claims

1. In an in-wheel motor housed within a wheel, the wheel includes a tire mounting portion on which a tire is mounted, and an in-wheel motor, characterized by including an annular fin formed on an outer circumferential surface in the circumferential direction of the in-wheel motor and forming a flow path through which air flows between the fin and the tire mounting portion.

2. The in-wheel motor according to Claim 1, characterized by including radial fins radially formed on an outer circumferential surface in the axial direction of the in-wheel motor.

3. The in-wheel motor according to Claim 2, characterized by connecting the radial fins and the annular fin.

4. The in-wheel motor according to Claim 3, characterized by arranging the annular fin axially inward of the outermost circumferential portion of a side plate portion of a housing of the in-wheel motor.

5. The in-wheel motor according to Claim 4, characterized by including a cylindrical portion where the annular fin is arranged and a side plate portion where the radial fins are arranged, and forming an inclined surface between the cylindrical portion and the side plate portion.

6. The in-wheel motor according to Claim 5, characterized in that the inclined surface is configured to intersect the side plate portion at 45 degrees or less.

7. In the in-wheel motor according to any one of Claims 3 to 6, characterized by making an outer diameter of the annular fin larger than an outer diameter of the radial fins.

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